


An Omega's Best Friend

by thursdayshunter



Category: Supernatural
Genre: Alpha/Beta/Omega Dynamics, Alternate Universe - College/University, Angst, Bestiality, Beta Dean, Bottom Castiel, Break Up, Community: spnkink_meme, Humiliation, Knotting, M/M, Omd, Omega Castiel, Other, Power Bottom Castiel, Riding, Rough Sex, Top Dean, the past cas/omc is briefly mentioned and not really important
Language: English
Status: Completed
Published: 2014-07-08
Updated: 2014-07-08
Packaged: 2018-02-07 23:56:13
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,710
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/1918959
Author URL: https://archiveofourown.org/users/thursdayshunter/pseuds/thursdayshunter
Summary: <blockquote class="userstuff">
              <p>It wasn’t that he didn’t enjoy sex with his boyfriend but Castiel honestly preferred a knot. He loved being stretched wider and plugged up while he was pumped full of his partner’s seed. Heats were far more tolerable as well but he wasn’t going to mention that to his boyfriend.</p><p>Castiel had gone into the relationship knowing a beta dick was far different than an alpha’s dick.</p><p>Spnkink-meme Prompt Fill</p>
            </blockquote>





	An Omega's Best Friend

**Author's Note:**

> This has Cas/Dog in it. If that isn't your kind of thing then you are better off exiting out of this fic and finding another one.
> 
> For description of prompt scroll down to End Notes.

“ _Fuck_...you’re so wet for me.” Dean breathed against Castiel’s neck as he thrust inside the omega. His fingers curled around his boyfriend’s wrists to hold them down and his thrusts picked up speed. “So good for me baby.” He pressed Castiel down into the sheets and used his body to hold him there as he kept thrusting forward.

Dean could feel his orgasm building, that delicious pressure at the base of his spine, as his pace fell off. He didn’t notice that Castiel was staring over at his dog standing in the doorway watching them. “ _Oh_.” Castiel’s mouth dropped open and his blue eyes clenched shut as he focused on the cock sliding against his insides.

Occasionally he felt Dean brush his prostate and the resulting pleasure had his breathing hitching, more slick aiding the beta’s way, but Castiel missed the catch of a knot on his rim. “Mmmmm. Love being buried inside you.” Dean’s body tightened as his cock jerked and he spilled into Castiel with a moan. “That’s it.” He relished how Castiel’s hole was clenching around him and the feeling of pleasure still rushing under his skin.

A few moments passed before he leaned back and reached between them to stroke at Castiel’s cock. He teased the head of the omega’s dick, pressing against the slit, while watching Castiel’s lips part. Soft pants escaped as Castiel tried bucking up into the hand on him.

Dean used the slick from earlier and the precome from Castiel’s cock to aid his motions as his hand kept steadily jacking Castiel off.

“Come for me baby. Let go.” He encouraged, green eyes staring at Castiel’s flushed cheeks, as he continued moving his hand and then Castiel’s body arched.

A soft moan slipped from Castiel’s lips as he came all over Dean’s hand while some of it ended up on his stomach. He felt himself go limp on the sheets, enjoying the low buzz of pleasure, as Dean continued to pin him and watch his features as he finally pulled out.

“Are you leaving?” Castiel inquired as he sat up, ignoring the come and slick leaking out of him, and watched Dean going to get a wash cloth to clean them up. He caught the one tossed to him and slowly moved to start cleaning the small mess on his stomach.

He would deal with the slick and semen later.

“I have to cover the late shift.” Dean looked annoyed by that fact, “I’d rather stay here.” And it was more than obvious in Dean’s tone he meant it. “We haven’t gotten much time together lately.”

“The semester will wind down.”

“Your heat is supposed to hit in a few weeks-“

Castiel arched a brow and climbed off his bed to stand before his beta boyfriend, “I know you have to pick up extra shifts. I have plenty of toys,” Dean looked about to protest, “I’m not your responsibility.” He spoke softly and offered a small smile. “I’ll be fine. If you can make it over that’s great but if not I’ll make sure I have plenty of supplies.”

Dean watched his features and relaxed, “Fine.” He stepped close and dragged his boyfriend in for a kiss, “I’ve heard how bad they can be and I don’t want you by yourself if you don’t have to be.” He pressed their foreheads together and then pulled away to finish dressing.

A quick kiss on Castiel’s lips and the beta was out the door with a grin. The second Castiel was sure Dean was gone he glanced over at his dog, a big mutt that Castiel had adopted a few years ago, with a grin. “Besides you’ve helped me through several heats haven’t you?” he crouched down and ruffled the dog’s fur with an affectionate smile. “Were you jealous someone else was fucking me?” Castiel had noticed the dark red head of his dog’s cock peeking out of its sheath. “It’s been a few days hasn’t it?” he glanced to the bed and shrugged.

Castiel rose to his feet before padding over towards his bed and he climbed up to move across the soiled sheets. The scent of slick and arousal was still thick in the air but Castiel ignored it and took a position in the center of the bed.

He didn’t typically offer up his ass in the traditional position of an omega presenting for Dean but for his dog, Conner, it was the only way to take his knot comfortably. “Come on.” He patted the bed and spread his legs better as he arched his back. “Up.”

They had done this enough that Conner only lapped at the slick leaking from Castiel for a little while before he was moving to mount his omega owner. Fur brushed against Castiel’s bare skin, legs gripped his sides and he shivered in anticipation.

It wasn’t that he didn’t enjoy sex with his boyfriend but Castiel honestly preferred a knot. He loved being stretched wider and plugged up while he was pumped full of his partner’s seed. Heats were far more tolerable as well but he wasn’t going to mention that to his boyfriend.

Castiel had gone into the relationship knowing a beta dick was far different than an alpha’s dick. And he loved having Conner’s knot inside him so it wasn’t a great loss.

“Come on boy.” He breathed and reached back to hold himself open in the hopes that Conner could get his cock inside in few strokes. “Fuck me good. Come on.” Castiel stopped breathing as he felt his dog’s cock bumping against him, slipping through his slick, as Conner kept thrusting forward until he finally caught himself just inside Castiel’s hole.

There was a second of stillness and then Conner was slamming inside Castiel with a hot huff of breath against his omega owner’s neck. Unlike Dean the dog’s thrusts were far harder, quicker and greedy in a single-minded way that only an animal or an alpha in rut could manage.

Conner’s dick pistoned inside Castiel’s wet hole, occasionally bumping the omega’s prostate and earning broken moans, as Castiel fought to maintain his position and hold the weight of the dog on top of him. “Good Conner.” Castiel moaned it, “Fuck me hard. Come on boy.”

The dog’s knot started to swell and the first time it tugged on Castiel’s rim he wanted to whimper. It was impossible not to miss an alpha knot after he’d been spoiled with a fuckbuddy in high school who helped Castiel through his heats.

The thrusts became rougher as the dog rutted against Castiel’s ass and when his knot was caught inside Castiel’s clenching hole the omega came across his sheets with a wail. Fingers clutched uselessly at the sheets but Castiel allowed himself to get lost in the pleasure of a knot stretching him open and the warm rush of hot semen starting to shoot inside him.

“Fuck.” He breathed out as Conner turned so he was ass-to-ass with his owner and his knot tugged on Castiel at the position.

The omega ignored the tug and allowed himself to collapse on the sheets as he waited out Conner’s knot. Part of him wished his dog’s knot lasted as long as an alpha’s but for now he was more than content to clench his ass around it and milk his dog for every single drop until they could separate.

He sighed out and rubbed his cheek against his pillow, sated and lazy, while he waited until Conner tugged free and turned to start enthusiastically lapping at the mess leaking from him.

The dog’s tongue brushed against Castiel’s puffy hole and had high little keens escaping.  Occasionally it slipped inside and tongued at Castiel’s insides. Each time it slipped inside Castiel jerked and shoved his face harder into his pillow until Conner hopped off the bed.

He lay there and waited until he felt like climbing off the bed to head into the bathroom to clean up. Satisfaction filled him completely and he sang lowly under his breath as he started washing himself under the hot shower. Castiel closed his eyes and stepped further under the spray to allow it to cascade down his body. “Still have to change the sheets.” He muttered it to himself as he finished up in the shower and stepped out to towel himself off.

It was then that he felt the light little cuts on his sides from Conner’s nails and resolved to be a little more careful. He didn’t want Dean asking where the scratches came from.

The weeks bled into months and Castiel made sure to wait for Dean to leave before indulging in a knotting from his dog. It didn’t matter that he wasn’t in heat during those times. Castiel simply enjoyed being stretched open and caught on his dog’s knot.

Currently Dean was twisting his fingers inside Castiel’s hole, occasionally brushing against the omega’s prostate, as he watched a flush spread across Castiel’s features. “Can’t wait to be inside you.” He twisted them again and slowly pulled his fingers out but before he could press Castiel down into the mattress to push inside the omega twisted and Dean found himself flat on his back.

There was a cheeky grin on Castiel’s face as he straddled Dean and pushed his ass back against his boyfriend’s cock. “You’re not controlling this show tonight, Dean.” He leaned down and pressed his lips to the beta’s while his fingers tugged on Dean’s hair. “I’m feeling like being on top.” The words brushed against Dean’s skin as Castiel pulled back and shifted himself so he could reach behind to grip Dean’s cock.

Carefully Castiel guided himself down onto Dean’s dick. He allowed his eyes to slip closed as he focused on taking every single inch, feeling it stretching him wider, until he had taken the entire length inside his body. The omega shifted himself and sighed at the feeling of full before pressing his hands on Dean to start moving.

He enjoyed being able to set the pace, pushing Dean down into the mattress, as he rode him and moaned. “Would you let me tie you up and ride you?” he asked, tightening down around Dean’s cock and pausing his in motions. “Would you let me have that kind of control?” it was a heady thought and it was causing his arousal to increase.

Castiel thought for a moment he could come just from the thought of being able to tie someone up and ride them until he got off. It had him moaning and leaning forward to grab onto Dean as his hips kept moving. “With you wrapped around me I’d probably agree to anything.” Dean admitted as he thrust up into the omega on top of him. A moan escaped him.

He tried to move his hand but Castiel pinned him to the sheets and paused in his movements. “No.” the word was almost growled and the sound went straight to Dean’s cock.

Instead Castiel shifted back and reached down to stroke himself, panting and moaning at the sensations, as he dragged himself closer and closer to his orgasm while still riding Dean.

“Oh oh yes.” Castiel hissed it out. His movements stuttered, fell off their rhythmic pace, as his ass tightened around Dean and his orgasm had him stilling as he came spattering Dean’s chest.

Warm hands gripped his hips and Castiel blearily looked down at Dean as the beta started to fuck up into him with a desperation that was pulling whimpers from Castiel whose body was sensitive after his orgasm. “Dean oh-“

“Fucking-“ Dean gritted his teeth and slammed up into Castiel as he came with a drawn out moan. His hold loosened until Castiel was sprawled out on top of him and nuzzling against his neck.

They lay there panting softly, both of them buzzing with the residual pleasure from their orgasms, until Castiel rolled off and sprawled out on his bed. He waited for the shift of the mattress as Dean got up and glanced sideways to watch the usual ritual Dean went through before he left for a late shift.

The sight had a slight frown tugging at his lips and to stifle the disappointment he looked to the side at a picture taken of the two of them on campus. He sighed and reached for one of his pillows to drag it close. “Cas?” Dean’s hand touched him and blue eyes glanced back to see a small frown on Dean’s features. “Something wrong?”

“No. Everything is fine. I’m just tired.” It was a lie but he wasn’t going to admit it. Instead Castiel was going to wait until Dean left and then he was going to have his dog fuck him on the floor. It was going to be filthy and rough and demeaning but he was going to have a knot buried in his ass and he’d love every second of it.

Right now he really just wanted a warm weight on top of him and a knot splitting him open. That’s all he wanted. It would push away the disappointment of watching Dean leave after sex.

That seemed to be all the two of them did after sex. They went their respective ways.

"Get some sleep. I’ll come back after my shift…its short tonight. They’re only having me cover for three hours.” he trailed off and left room for Castiel to object but nothing came. “Goodnight.” Dean murmured and padded out of the room. He felt Conner brush by him and ignored the dog as he moved through the apartment before heading outside to his car.

Castiel allowed himself to slip into a light doze.

Almost two hours later he rolled over and looked over at his dog who was lying next to him on the bed. “Hey Conner.” He reached out a hand and stroked down the dog’s soft fur. A warm tongue licked him and it had a smile tugging at his lips.

Castiel twisted away and climbed out of bed. He stretched, sighing at his muscles pulled and loosened, before he turned to see his dog staring at him.

The dog’s eyes tracked his movements and a quick glance to the clock revealed he had some time before Dean came back home. Castiel could see Conner’s cock coming out of its sheath as the dog scented the air and the pure focus in those eyes had his body responding.

He really wanted a knot in his ass and he had plenty of time before Dean came home. Enough time to email his assignment, come back into his bedroom for a rough fucking on the floor and then a quick shower.

Castiel padded out of the room and towards his laptop. He didn’t bother sitting down and instead leaned so he could bring up his email, attach the document and send. “There.” He grinned at the screen and moved back down the hallway towards his bedroom.

Conner followed him every single step of the way and when Castiel easily sank down to his knees, leaning forward to arch his back and start working his fingers inside his ass the dog stayed right there. Castiel could feel the body heat coming off the creature and grinned as his fingers started to pump inside his hole.

He could feel slick and how his fingers occasionally brushed against his prostate to send pleasure through him. “Fuck.” He quickly pulled his fingers from his ass and spread his cheeks wide, pushing his ass up a little, as he braced himself. “Up Conner. Up boy.” He didn’t want to waste time and the furry weight pressing him down signaled that Conner was in agreement.

The jabs were short and quick as the dog desperately sought the wet hole in front of him. He slipped in the slick until Castiel, impatient, reached back to help him and the second Conner’s cock slipped inside the omega moaned.

Conner wasted no time in thrusting forward, hard, as he started to rapidly fuck into the now moaning omega under him. Castiel knew that to his dog he was nothing but a bitch to breed and that thought alone had his cock aching. He loved the way Conner’s legs gripped him and the dog’s hips quickly thrust forward against him as his dog worked towards his knot.

“Oh oh yes there yes.” He tightened down and received a low growl but Castiel could already feel Conner’s knot forming and excitement had him spreading his legs for a better position. He could feel the knot popping in and out of his rim, tugging on it and pulling whimpers, until it finally caught and swelled to press against his insides.

His hand flew down to grip his cock and Castiel had himself coming on the floor with two strokes as his dog’s cock spilled inside him. For a moment Conner simply allowed his body to rest on top of Castiel, pressing the omega down, until he shifted and moved to put them ass-to-ass.

“Finally.” Castiel breathed with a pleased sigh. He had been itching most of the day for his dog’s knot and now Conner was caught inside him.

He lost track of time until eventually he realized that Conner’s knot was still locked inside him and didn’t seem to be going down.

“What the fuck?” Castiel shifted himself and heard a low growl when the motion pulled on Conner’s knot. He glanced at the clock and cursed. “Fuck.” Blue eyes darted around the room but he had been so lost in the feeling of full that he hadn’t heard the front door open and close. He hadn’t heard Dean come back to his apartment early.

Now Castiel was trying to figure out what to do until a voice caught his attention. “What the fuck is going on?” Dean stood in the doorway staring at them.

The first thing Castiel recognized was shock on his boyfriend’s face. He could see the way Dean’s mouth dropped open and how Dean’s eyes were staring at the place his dog was locked into him. “Dean I-“ he was cut off by a growl that was uncharacteristic of his boyfriend.

“Your dog?” the shock was rapidly changing into anger and disgust. “Are you that desperate for a _knot_ that you’ll be a dog’s bitch? That you’ll get down on the floor, on your knees, to let an _animal_ fuck you?” Dean’s lip curled up and Castiel wanted to stand but he was stuck on the floor. “I guess what they say about omegas is true. They’ll roll over for anything with a knot.”

“Dean that isn-“ he was cut off by a violent motion from the beta.

“No Cas! I don’t want to fucking hear it. Is this why you never worry if I’m not available to help you during your heats? You have a ready knot living with you all the time.” Dean turned his glare onto the dog, “A _dog_. A mutt you rescued.” His hands clenched.

“Why won’t you-“ Castiel bit back a growl of his own when Dean stepped right up to him and it had Conner trying to move away only to tug too hard on Castiel. Pain at the sudden motion had blue eyes clenching shut and the omega gritted his teeth to hold back the pained sound.

But Dean wasn’t done.

“Maybe we should just tie your slutty little ass down and film you getting fucked by a bunch of dogs? Would that make you happy? You could have a whole group of dogs panting after your ass and they could knot you one after the other until you have dog semen running down your legs. I’m sure people would pay to see what an omega bitch getting fucked looks like.”

Humiliation had Castiel’s cheeks flushing and he almost sobbed in relief when Conner’s knot _finally_ slipped from his ass. He staggered up to his feet, forced himself to ignore the feeling of semen leaking from him, as he tried to step closer to Dean. “Please just listen to me!” his voice cracked but Dean stepped away from him.

“Why? Why should I listen to someone who has been lying to me the entire time we’ve been going out?” Dean tilted his chin up, “If you wanted a knot so badly why on Earth would you agree to go out with me? Why would you ever start up a relationship with a _beta_?”

“Because I liked you!” the words burst out, “You were different and I liked you.” He trailed off and mentally cursed himself.

“You let your dog fuck you when I’m not around. You present your ass to an animal and let him use you.” Dean’s features still held disgust, “We’re done. Find yourself another idiot to agree to some kind of fucked up relationship because I’m not sticking around for this. I can find someone who doesn’t care if I have a knot or not.”

Castiel’s mouth dropped open and he watched Dean storm out of the room, slamming the door violently behind him, as he stalked through the apartment and right out the door. A loud bang let Castiel know his now ex-boyfriend had slammed that shut as well. “Fuck.” He tugged at his hair and cursed himself for his stupidity. “Fuck.” He sank to the ground and ignored the mess he was making. “Knew that was going to happen. Fucking knew it.”

He felt the annoying signal that his face heating up and a prickling at the backs of his eyes made itself known but Castiel ignored that and focused on controlling his breathing. He would be fine. He would get through this and he could find someone else.

“I’ll be fine.” He muttered to himself and tugged on his hair harshly until it had him gasping in pain. “It’s ok.” But the humiliation from Dean’s words, from being caught in such a shameful act, was still simmering inside him and he fought to ignore that as well. He ignored the way his breathing hitched and tears started to stream down his cheeks as the first of many sobs bubbled up from his chest to escape into the still room.

**Author's Note:**

> Spnkink-meme prompt:
> 
> Cas isn't in heat or anything, he just loves having his dog's knot inside him. It's not something he can get from his beta boyfriend. Only this time something isn't right... for some reason the knot won't go down and they're stuck together for way longer than usual. Dean catches him and it isn't pretty.
> 
> http://spnkink-meme.livejournal.com/86610.html?thread=33505106#t33505106


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